A MIMO (Multiple-Input Multiple-Output, multiple-input multiple-output) system is a system that allows multiple antennas to send and receive signals at the same time; because there are many antennas in the MIMO system, all the antennas in the MIMO system use a power amplifier with relatively low power, and the MIMO system is widely applied nowadays as an increasingly high requirement is imposed on an energy-saving indicator. When a signal is transmitted by using the MIMO system, a transmit end needs to preprocess an input signal, so as to reduce an impact of multipath fading on the signal. The multipath fading refers to a phenomenon that, being affected by terrestrial and atmospheric refraction in a transmission process, a signal arrives at a receive end through multiple different paths; and includes flat fading and frequency selective fading. A flat fading channel has a basically same impact on amplitudes and phases of signals with different frequencies, and a frequency selective fading channel has different impacts on amplitudes and phases of signals with different frequencies.
Preprocessing the input signal by the transmit end includes precoding, RE (Resource Element, resource element) mapping, and IFFT (Inverse Fast Fourier Transform, inverse fast Fourier transform). The precoding refers to preprocessing a frequency-domain signal in a case in which channel state information is known, so as to reduce interference. The RE mapping refers to mapping a frequency-domain signal on a subcarrier to a corresponding subcarrier in a physical resource block. The IFFT refers to transforming a frequency-domain signal into a time-domain signal.
Specifically, the transmit end performs time sampling on the input signal, and obtains one time sampling point from each antenna; calculates a constraint matrix according to a flat fading channel characteristic; presets a predetermined quantity of iteration times required for calculating an output signal, and initializes the output signal to 0; calculates an intermediate variable, and performs a peak clipping operation on an obtained intermediate variable; detects whether a current quantity of iteration times reaches the predetermined quantity of iteration times; and if the current quantity of iteration times does not reach the predetermined quantity of iteration times, uses an intermediate variable obtained after the peak clipping operation as an input signal for a next time of iteration; or if the current quantity of iteration times reaches the predetermined quantity of iteration times, determines an intermediate variable obtained after the peak clipping operation as the output signal. The output signal is obtained according to the constraint matrix and the peak clipping operation; therefore, a PAR (Peak to Average Ratio, peak-to-average ratio) of the output signal is relatively small, that is, an instantaneous value of the output signal is within a linear working area of an amplifier, which avoids non-linear distortion of the signal caused when the instantaneous value is beyond the linear working area.
In a process of implementing the present invention, the inventors find that at least the following disadvantage exists in the prior art:
A constraint matrix in the prior art is calculated according to a flat fading channel characteristic, but a broadband system using an OFDM (Orthogonal Frequency Division Multiplexing, orthogonal frequency division multiplexing) technology is affected by frequency selective fading; therefore, the prior constraint matrix is not applicable to an OFDM symbol, and the OFDM symbol cannot be preprocessed. The OFDM is a multi-carrier modulation scheme in which a carrier can be divided into several orthogonal subcarriers, a high-speed serial data stream is converted into low-speed parallel sub-data streams, and the low-speed parallel sub-data streams are modulated to each of the subcarriers for transmission, where each OFDM symbol includes at least one modulated subcarrier.